1. Field of the Invention
The present invention relates to extruded styrene-acrylonitrile polymer foam and a process for preparing such foam.
2. Description of Related Art
Preparing extruded polymer foam that has desirable skin quality is challenging when using water as a blowing agent. Water tends to cause undesirable pinholes (also known as blowholes) that can disrupt a foam surface. Prior art references offer some ways to reduce undesirable effects of an aqueous blowing agent in preparing extruded foam.
PCT publication WO2008140892 discloses that use of a styrene-acrylonitrile (SAN) copolymer having a polydispersity index less than 2.5 in combination with a blowing agent comprising water and a fluorinated compound can produce polymer foam having a good skin quality that is free from blowholes.
U.S. Pat. No. 5,380,767 discloses that increasing the water solubility of a styrenic polymer composition or including an additive into the styrenic polymer composition that enhances the water solubility of the styrenic polymer composition can produce a closed-cell, monomodal foam from the styrenic polymer even with an aqueous blowing agent.
It is desirable to further advance the art of preparing extruded thermoplastic polymer foam using an aqueous blowing agent over these known methods.